The present invention relates to multifilament superconductors whose electrical performance under superconductive conditions has been stabilized and which are made of brittle, prereacted Nb.sub.3 Sn filaments in a bronze matrix and to a process for producing such stabilized multifilament superconductors.
The use of prereacted Nb.sub.3 Sn/bronze multifilament superconductors in the construction of high field magnets is fraught with uncertainties since the known brittleness of Nb.sub.3 Sn/bronze conductors may produce inadvertent defects in the conductor when it is produced and also while the magnet is being constructed. These defects then bring about a reduced current carrying capability of the conductor and thus reduced power of the constructed magnets. Without discussing the particular problem of possible defects in the conductor, at present it is exclusively copper which is integrated in the conductor for stabilization purposes with the superconductive multifilaments occupying a cross-sectional area up to 60% of the conductor and the copper occupying a cross-sectional area of at least 40% of the conductor. In special conductor designs, copper profiles are soldered on so as to produce larger copper area proportions. See, for example, H. Kuckuck, E. Springer and G. Ziegler, CRYOGENICS, June 1976, pages 350 to 354.
Due to the high magnetoresistance of copper, the required copper area proportion is large. This results in a reduction of current density. Therefore, it becomes almost impossible to accommodate a steel armor in the conductor. Accordingly, if copper is used for stabilization, it must further serve as an armor or force carrying element and therefore must be in a semihard state.